Radiation therapy is used for various medical applications, such as combating cancer, for example. Generally, speaking when irradiating a subject, it is desirable to impart a prescribed radiation dose to the diseased tissue (referred to as the “target” or “target volume”), while minimizing (to the extent possible) the dose imparted to surrounding healthy tissue and organs. Various systems and methods have been devised for delivering radiation while trying to achieve this objective. Such systems and methods generally involve: obtaining one or more images of a region of interest (including the target volume) in the subject's body; initializing a radiation treatment plan; adapting or optimizing radiation delivery variables in effort to achieve the objectives of the treatment plan; and delivering radiation. These procedures are illustrated in FIG. 1.
One drawback with current techniques is the time taken between the imaging procedure and completion of the radiation delivery procedure. The imaging procedure may involve obtaining a computed tomography (CT) image for example. The time between completing the imaging procedure and starting the radiation delivery procedure may typically be on the order of a week or two. Moreover, radiation delivery typically involves several discrete steps referred to as “fractions”. By way of example, a treatment plan may be divided into 10 fractions and a subject may receive one fraction every day for 10 days. Thus, it may take on the order of several weeks to a month (or more) between the imaging procedure and completion of the radiation delivery procedure.
The characteristics of the target volume (e.g. the size, shape and/or location of the target volume) and the characteristics of the healthy tissue (e.g. the size, shape and/or location of the healthy tissue relative to the target volume) can change over time. By way of non-limiting example, a tumor in a subject's lung commonly moves whenever the subject breathes and a tumor in a subject's prostate may be deformed by changes in the shape of the bladder and/or the rectum. Because the likelihood of changes in the characteristics of the target volume and/or the characteristics of the healthy tissue increases with time, the time between imaging and radiation delivery represents a significant limitation to the general desire of imparting a prescribed radiation dose to the target volume, while minimizing (to the extent possible) the dose imparted to surrounding healthy tissue and organs.
Newer radiation delivery systems and methods referred to as “on-line” adaptive radiation therapy (ART) have attempted to reduce this time between the imaging and radiation delivery procedures. In on-line ART techniques, each of the FIG. 1 procedures is implemented for each treatment fraction. That is, for each fraction (e.g. each time that the subject comes to the hospital), the subject is subjected to serially implemented imaging, initializing, optimizing and radiation delivery procedures. Because on-line ART techniques involve a separate imaging procedure (for each fraction) and radiation is delivered (for each fraction) relatively soon after imaging, the characteristics of the target volume and the healthy tissue are less likely to change between the imaging and radiation delivery procedures of each fraction. Accordingly, on-line ART has achieved some success at addressing the general desire of imparting a prescribed radiation dose to the target volume, while minimizing (to the extent possible) the dose imparted to surrounding healthy tissue and organs.
These gains achieved by on-line ART have not come without cost. For on-line ART, the subject is typically required to be stationary on the treatment couch (or at least in the treatment facility under the care of medical staff) for the entirety of each fraction (i.e. for each iteration of the imaging, initializing, optimizing and radiation delivery procedures). Also, current on-line ART techniques are expensive to implement because it takes a relatively long time to implement each fraction. Treatment of each subject using on-line ART occupies the radiation delivery system and other hospital resources (e.g. medical staff, rooms etc.) for a relatively large amount of time. In addition, the subject is required, for each fraction, to spend a relatively long time at the treatment facility which is generally undesirable.
There is a general desire to reduce the amount of time required for each iteration (i.e. each fraction) of on-line ART techniques.